AIRBORNE SPECTROMETER MEASUREMENTS FROM BOREAL AND TUNDRA SITE DURING SPRING SNOW MELT

Sampling: The airborne hyperspectral data were acquired with an AisaDUAL imaging spectrometer manufactured by Spectral Imaging Ltd (SPECIM). The airborne spectral measurements were made from airplane at an altitude of 800 m offering a spatial resolution of 0.8 m and a swath of 240 m. Flight lines were several kilometers long. The instrument foreoptic unit was set to look at nadir (0 degrees) and the field of view (FOV) was 17 degrees. The Oxford Technical Solutions RT4000 GPS/INS was utilized to provide high accuracy position measurements with low drift rates. The reflectance level was obtained by applying a real-time fibre optic downwelling irradiance sensor (FODIS). The measurements from Sodankylä were carried out in direct illumination (i.e. clear sky: 0/8) and the measurements from Saariselkä were carried out in diffuse illumination (i.e. cloudy sky: 7/8). Processing: The AisaDUAL spectrometer data was radiometrically and geometrically corrected by using the SPECIM's CaliGeo tool in the ENVI software. Measurements from Saariselkä are additionally corrected with the digital elevation model KM10 with a pixel size of 10 m × 10 m and elevation resolution of 1.4 m. The original spectral resolution for the VNIR bands was 5 nm and for SWIR bands 6 nm totaling to 359 spectral bands. The original spatial resolution of the data is 80 cm x 80 cm. From this data the bands 555 nm, 645 nm, 858.5 nm and 1640 nm were extracted from the spectra by using the band specific FWHM criterion (Full width at half maximum) corresponding to MODIS bands. For these bands the data was filtered with mean filter using 12x12 window corresponding to pixel size of 10 meter.